This invention is in the field of stepping type motors generally utilized in connection with machine tool control, and specifically for exact shaft angular positioning of the rotor when used for controlling the print cycle of an impact typewriter head printer.
U.S. Pat. No. 3,667,383 directed to a print head control circuit has the disadvantage of having to utilize two rotating wheels to obtain a differential output in terms of character counts. This patent also does not utilize rapid electrical braking action by failing to provide for equal and opposite torques in a polyphase motor structure.
U.S. Pat. No. 3,757,192 has a control circuit directed to a numerical feed control. Though applicable to an electric typewriter with substantial modification, this patent is basically dependent upon dual pulse motors for obtaining the numerical control. This patent also has the shortcomings mentioned in connection with U.S. Pat. No. 3,667,383, above.
U.S. Pat. No. 3,761,790 is for a control circuit for moving a shaft to a predetermined angular position. This patent utilizes a motor in periodic cooperation with an electromechanical brake to stop the shaft. The motor is a conventional type, having a coupling and brake winding in parallel hard wire connection to each other. As in the case of U.S. Pat. No. 3,757,192, this patent also has the shortcomings mentioned in connection with U.S. Pat. No. 3,667,383.
U.S. Pat. No. 3,757,191 is directed to a polyphase motor control circuit of a stepping motor. However, though utilizing pulses to obtain the several phases to enable a rotating field to be thereby obtained, the motor therein does not have two torques exerted at the rotor in equal and opposite directions for enabling rapid and accurate braking action. Rather, this patent utilizes different and complex pulse train sequences to accomplish stopping of the rotor. This patent involves complex electronics and built-in unreliability due to the number and types of circuts used. In addition this patent also suffers from the shortcomings mentioned in connection with U.S. Pat. No. 3,667,383, above.
U.S. Pat. No. 3,798,526 is for a high speed stepping motor. This patent requires the use of a commutator as part of a wound rotor assembly. Electronic circuts are used to reverse direction of the field of the motor by reversing polarization of the rotor or the stator. Consequently, this patent does not have the advantage of two simultaneous equal and opposing torques to provide instantaneous rotor braking as might be created by two oppositely rotating fields, and hence also suffers from the same shortcomings mentioned in connection with U.S. Pat. No. 3,667,383, above.